$20-$28, however, is much more my speed because I tend to get bored of them after 2-3 years. Luckily, I just discovered that Society 6 has expanded their offerings to include 16-20" pillow covers!
There are literally hundreds to choose from, and if your taste skews modern, you'll be thrilled. All are available in three sizes and sold with or without an insert. You can restyle a whole couch for under $100!
Here are my favorites: